Multi-stage process for preparing N-alkyl-3,4-dialkyl-2,6-dinitroanilines

ABSTRACT

A multistage process of preparing N-alkyl-3,4-dialkyl-2,6-dinitroanilines starts from 3,4-dialkyl phenol and goes through the stages of 3,4-dialkyl-2,6-dinitrophenol and 3,4-dialkyl-2,6-ditro alkoxybenzene, wherein the latter are new compounds.

This is a division of parent application Ser. No. 08/264,450, filed Jun.23, 1994 (now U.S. Pat. No. 5,475,148).

BACKGROUND OF THE INVENTION

The present invention concerns the improved process for preparingN-alkyl-3,4-dialkyl-2,6-dinitroanilines. The present invention moreparticularly concerns a commercially viable process to prepare thecompound pendimethalin, (known by the chemical nameN-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine) its derivatives and itsintermediates.

Pendimethalin and its derivatives are reported by U.S. Pat. No.4,066,441 as excellent pre-emergent herbicides.

Several procedures are reported in the literature to prepare thesecompounds. The last step in preparing the compound pendimethalin isreported by U.S. Pat. No. 3,920,742 to involve the nucleophilicsubstitution of 3,4-dimethyl-2,6-dinitrohalobenzene (especially thechloro derivatives) with the appropriate amine, thus: ##STR1## where thechloro-intermediate was prepared in one of several problematicmulti-step processes beginning with o-xylene, as follows:

o-Xylene is first chlorinated to form 4-chloro-o-xylene, which in turnis nitrated with fuming nitric acid to give the3,4-dimethyl-2,6-dinitro-chlorobenzene in a yield of 27%. First of all,the low yield is not commercially viable. Secondly, the chlorinationstep affords a mixture of chloro isomers, requiring the distillation ofthe product mixture to separate the 4-chloro- isomer from its 3-chloroisomer with only great difficulty due to their very close boilingpoints. Finally, the low yield of the nitration step stems from the needto purify the 3,4-dimethyl-2,6-dinitro-chlorobenzene from dangeroushigher nitrated by products. This alone makes this process difficult forcommercialization.

A second process, illustrated by U.S. Pat. No. 4,123,250, involvesnitrating 3,4-dimethylaniline to form 3,4-dimethyl-2,6-dinitroanilinewhich is then reacted via a Sandmeyer reaction to form3,4-dimethyl-2,6-dinitro-chlorobenzene. This process suffers from lowyields and requires the laborious separation from various by-products.

A third process, illustrated by U.S. Pat. No. 4,199,669 and U.S. Pat.No. 4,261,926, is based on the reductive alkylation of3,4-dimethylaniline with a ketone or directly from 4-nitro-o-xylene,thus: ##STR2## and the product is subsequently nitrated withconcentrated nitric acid to give the 2,6-dinitro derivative. Thisprocess suffers from the fact that the preparation of the4-nitro-o-xylene always is accompanied by the 3-nitro derivative, andtheir separation is very difficult.

Several improvements have been reported in attempts to overcome theabove described problems. Thus, U.S. Pat. No. 3,929,916 and U.S. Pat.No. 3,929,917 disclosed the use of mercury salts or nitrogen tetroxideto avoid the formation of unwanted by-products. However, these catalystsare poisonous and dangerous materials requiring special handling.

U.S. Pat. No. 4,119,669 and U.S. Pat. No. 4,201,926 report the use ofnoble metal catalysts. But such catalysts are very expensive with lossesduring the process.

According to U.S. Pat. No. 4,136,117; and U.S. Pat. No. 4,621,157 thenitration of N-alkyl-zylidine leads to three products:

1. N-Alkyl-3,4-dimethyl-2,6-dinitroaniline:

2. N-Nitroso-N-alkyl-3,4-dimethyl-2,6-dinitroaniline; and

3. N-Nitro-N-alkyl-3,4-dimethyl-2,6-dinitroaniline.

The formation of toxic nitroso compounds makes it imperative to lowerthe concentration of these compounds to very low levels. As a result, adenitrosation process (as described in U.S. Pat. No. 4,134,917 and U.S.Pat. No. 4,136,117) and denitration process (as described in U.S. Pat.No. 4,391,992) are required in order to obtain commercially usefulproduct. However, it is preferable to use a process to preparependimethalin and its analogues which avoids the formation of such toxicnitroso compounds.

OBJECTIVES OF THE INVENTION

It is the objective of the present invention to provide a new andimproved method for the preparation ofN-alkyl-3,4-dialkyl-2,6-dinitroanilines and their intermediates. It is afurther objective of the present invention to provide a method for thepreparation of these compounds avoiding the above mentioned disadvantagewithout having to handle highly toxic or dangerous compounds. A furtherobjective is the provision of a commercially viable method for thepreparation of these compounds in high yields.

SUMMARY OF THE INVENTION

It has unexpectedly been discovered that N-alkyl-3,4-dialkyl-2,6-dinitroanilines of the formula ##STR3## Wherein R₁ is hydrogen, C₁to C₆ straight or branched chain alkyl group and

R₂, R₃ and R₄, are independently C₁ to C₆ straight or branched chainalkyl group optionally substituted by one or more halogen groups, may beprepared comprising the steps of:

1. Reacting 3,4-dialkyl phenol with nitric acid in a two phase system toform 2,6-dinitro-3,4-dialkyl phenol;

2. Alkylating the 2,6-dinitro-3,4-dialkyl phenol by reacting with analkylating agent preferably in the presence of a catalytic amount of aphase transfer catalyst chosen from the group consisting of

    (R').sub.4 Q.sup.+ X--

wherein R' may be the same or different C₁ to C₁₆ straight or branchedalkyl groups, benzyl, substituted benzyl;

Q is N or P: and

X is Cl, Br, I or HSO₄ :

a macrocyclic ether and polyethylene glycols of formula

    HO--(CH.sub.2 CH.sub.2 O--).sub.n --CH.sub.2 CH.sub.2 OH

where n is an integer from 10 to 50 to form 2,6-dinitro-3,4-dialkylalkoxy benzene.

3. Reacting the 2,6-dinitro-3,4-dialkyl alkoxy benzene with an amine inthe presence of a catalytic amount of base or halide to formN-alkyl-3,4-dialkyl-2,6-dinitroaniline; and

4. Recovering the N-alkyl-3,4-dialkyl-2,6-dinitroaniline formed.

DETAILED DESCRIPTION OF THE INVENTION

The reaction process is generally illustrated below on a batch-wisebasis: ##STR4##

Examples of alkyl groups of groups R₁, R₂, R₃, R₄ and R₅ are methyl,ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, 1-methylpropyl, 1-ethyl propyl, 1-methylbutyl, 1-ethylbutyl, and the like.

Stage I involves a direct and improved process to nitrate 3,4-dialkylphenol with a minimum of by-products. This is effected using a two-phasesystem of an organic solvent and an aqueous nitric acid solution.Nitration of phenols using a two phase system has already been disclosedin East German Patent Number 12,348; West German Patent Number1,092,025; and U.S. Pat. Nos. 2,802,883 and 4,621,157 using differentconditions and different phenols.

In practice, a solution of 3,4-dialkyl phenol in an organic solvent isslowly added to the aqueous solution of nitric acid at a temperature offrom 10° C. to 40° C. over a period of 3 to 6 hours. The molar ratio ofphenol to nitric acid may be 1:2 to 1:4, but preferably from 1:2 to1:2.5. The reaction is carried out preferably at atmospheric pressure,when the concentration of nitric acid may be 15% to 55%, preferably 20%to 50%.

The organic water-imiscible solvent may be any chlorinated aliphatic oraromatic derivative the phenol is soluble in. Examples aredichloromethane, 1,2-dichloroethane, 1,1,1-trichloroethane, carbontetrachloride, chloroform, trichloroethylene, tetrachloroethylene,chlorobenzene, dichlorobenzene, benzene, dialkylethers and mixtures ofthese.

The resulting reaction mixture may be worked up by separating the twophases and the nitrated product in the organic phase is separated bystandard means. The aqueous acidic phase may be reused in this processafter adjusting the concentration with fresh concentrated nitric acid.

The 3,4-dialkyl phenol may be either commercially available, as in thecase of 3,4-xylenol or prepared from 3,4-dialkyl benzenesulfonic acid asdescribed in SU 577,202 and CZ 159,631. The 3,4-dialkyl benzenesulfonicacid may be prepared by the sulfonation of o-dialkyl benzene accordingto Czech Patent Number 163,030.

Stage II involves an alkylation of the hydroxylic group, namelyO-alkylation. This reaction can be carried out using alkylating agentssuch as alkyl sulfate, alkylarylsulfonates or alkyl halides. Dimethyland diethyl sulfates are preferred. The reaction is carried out in thepresence of bases such as alkali hydroxides, alkali carbonates, oralkali hydrogen carbonates, with alkali carbonates preferred.

The second stage is preferably run in the presence of a phase transfercatalyst. Preferred examples are tetra(aralkyl)-alkylammonium halidessuch as didecyldimethyl ammonium chloride, tricaprylmethyl ammoniumchloride, benzyltrimethyl ammonium chloride, tetrabutyl ammoniumchloride, triethylbenzyl ammonium chloride and the like. Most preferredare didecyldimethyl ammonium chloride, tricaprylmethyl ammonium chlorideand triethylbenzyl ammonium chloride.

This stage is carried out in an organic solvent. This solvent may be analiphatic ketone (as acetone, methylethyl ketone, methylisobutyl ketoneand the like), a cycloalkylketone (as cyclohexanone, cyclopentanone andthe like), haloalkanes (as dichloromethane, 1,2-dichloroethane,methylchloroform, carbon tetrachloride and the like), an aromatichydrocarbon (as benzene, toluene, xylene and the like), a cycloalkane ascyclohexane and mixtures of these. Haloalkanes are preferred with1,2-dichloroethane most preferred.

The reaction of Stage II is run at a temperature of from 40° C. to 90°C., preferably from 60° C. to 80° C.

Stage III involves the reaction of the alkoxy 2,6-dinitro-3,4-dialkylbenzene in a nucleophilic substitution (SNA_(r)) with the appropriateamine. The reaction is run neat (no solvent) with a molar ratio of amineto phenol derivative of from 2:1 to 6:1, preferably from 3:1 to 5:1, ata temperature of from 20° C. to 40° C. The excess amine can be reusedafter distilling off at the end of the reaction.

The reaction of Stage III was found to be catalyzed by bases chosen fromthe group consisting of alkali hydroxide (as sodium hydroxide, potassiumhydroxide, lithium hydroxide), and halogenides as (calcium chloride,barium bromide and lithium chloride preferably calcium chloride) bylowering the reaction time to about 24 hours. The amount of catalystadded is one mole percent to 6 mole percent, preferably 3 mole percentto 5 mole percent, catalyst per mole alkoxy benzene derivative.

While the invention will now be described in connection with certainpreferred embodiments in the following examples, it will be understoodthat it is not intended to limit the invention to these particularembodiments. On the contrary, it is intended to cover all alternatives,modifications and equivalents as may be included with the scope of theinvention as defined by the appended claims. Thus, the followingexamples which include preferred embodiments will serve to illustratethe practice of this intention, it being understood that the particularsshown are by way of example and for purposes of illustrative discussionof preferred embodiments of the present invention only and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of procedures as well as of theprinciples and conceptual aspects of the invention.

EXAMPLE 1

Preparation of 2,6-dinitro-3,4-xylenol

A mixture of 630 grams (5 moles/ of a 50% aqueous nitric acid and 400 mldichloromethane were introduced in a two liter flask fitted with astirrer, a reflex condenser, a dropping funnel and a thermometer. Tothis stirred mixture was added dropwise a solution of 245 g (2 moles)3,4-xylenol in 400 ml dichloromethane, during two hours, maintaining thetemperature at 20°-25° C. After another hour stirring at the sametemperature the reaction mixture was heated to reflux (about 40° C.)until the starting product and the two intermediate products(2-nitro-3,4-xylenol and 4-nitro-3,4-xylenol) have disappeared (followedby GC analysis). This occurs in about three hours. The mixture wascooled to ambient temperature and allowed to separate in two phases. Thelower organic phase was separated from the aqueous acidic layer andwashed twice with water. Water (400 ml) was added to the organic phaseand dichloromethane was removed by distillation. The slurry of thedinitro compound in water was cooled and filtered and dried at 70° C. Aproduct of 93.7%. 2,6-dinitro-3,4-xylenol pure was obtained which was74.5% of the theoretical yield. After crystallization from ethyl alcoholit has a melting point of 124°-125° C.

EXAMPLE 2

Example 1 was repeated but, after washing of the organic phase withwater, the dichloromethane was recovered by distillation leaving theresidue of 2,6-dinitro-3,4-xylenol. The crude product was dissolved in a6 percent solution of sodium hydroxide and thereafter acidified with3,5-N-hydrochloric acid. The precipitated solid was filtered, washedwith water and dried at 70° C. It was obtained as product with meltingpoint of 120°-122° C.

EXAMPLE 3

Preparation of 2,6-dinitro-3,4-dimethyl anisole

A solution of 226 g, 2,6-dinitro-3,4-xylenol, 93.7%. (1 mole) in twoliters 1,2-dichloroethane was placed in a three liter reaction flask.Sodium carbonate 128 g (1.2 moles) and 0.81 g Didecyldimethyl-ammoniumchloride (DDAC) were added to the above solution and afterwards 151.3(1.2 moles) of dimethylsulfate were introduced during 15 minutes at theambient temperature. The reaction mixture was heated with stirring toreflux during two hours. Water (400 ml) was added and heating wascontinued for another hour. This mixture was cooled to 25° C. andallowed to separate in two phases. The lower organic phase wasseparated, washed with water to neutral.

The solvent was next recovered by distillation and the remaining oilyproduct solidified by cooling. A product (225.8 g) of 94%.2,6-dinitro-3,4-dimethylanisole was obtained at a 93.9% of thetheoretical yield based on 2,6-dinitro-3,4- xylenol consumed.Crystallization from ethyl alcohol gave a product with a melting pointof 67.3°-67.6° C.

EXAMPLE 4

Example 3 was repeated in every detail except that sodium carbonate wasreplaced by potassium carbonate. The yield of2,6-dinitro-3,4-dimethylanisole was 95%.

EXAMPLE 5

Example 4 was repeated except that didecyldimethylammonium chloride wasreplaced with tricaprylmethyl ammonium chloride (Aliquat 336). The yieldobtained was essentially the same.

EXAMPLE 6

Preparation of 2,6-dinitro-3,4-dimethylanisole

2,6-dinitro-o-xylenol (0.1 mole) was dissolved in 200 ml acetone towhich 0.12 moles potassium carbonate and 0.4 g triethylbenzylammoniumchloride were added. Next 0.12 mole dimethylsulfate were added duringten minutes and the mixture was heated to reflux during 1 hour. Water(40 ml) and 7 g potassium carbonate were added to the reaction mixtureand heating to reflux was continued for half an hour. Acetone wasremoved from the reaction mixture by distillation and to the residuewere added with stirring 80 ml DCM and 100 ml water. The organic phasewas washed with water to neutral and evaporated to obtain the2,6-dinitro-3,4-dimethyl anisole with a yield of 94%.

EXAMPLE 7

Preparation of 2,6-dinitro-3,4-dimethylphenetol

Example 5 was repeated except that 2,6-dinitro-3,4-xylenol was reactedwith diethylsulphate 185 g (1.2 mole). There was obtained 2.6dinitro-3,4-dimethyl phenetole with a yield of 94%. Crystallization fromethyl alcohol gave a product with a melting point of 64°-66° C.

EXAMPLE 8

Preparation of N(1-ethylpropyl)-2,6-dinitro-3,4 xylidine

To a suitable reaction vessel equipment with a thermometer andmechanical stirrer was introduced 24 g 2,6-dinitro-3,4-dimethylanisole94% (0.1 moles), 0.55 g C_(a) Cl₂ (0.005 moles), and 43.5 g (0.5 moles)1-ethyl propylamine. The reaction mixture was stirred at a temperatureof 25°-30° C. The progress of the reaction was followed by periodicallywithdrawing samples and analyzing for starting product and the newproduct formed. During 24 hours the starting product disappeared and theN-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitroaniline is gradually formed.After completion of the reaction as indicated by vapor phasechromatography, the excess of 1-ethyl-propylamine was recovered from thereaction mixture by distillation. The residue was dissolved indichloromethane and the solution was successively washed with 5% aqueoushydrochloric acid, 5% aqueous sodium hydroxide and then by water toneutral and dried. The solvent is next recovered by distillation leavingan oily product which solidified. (25.2 g 96.6%) with a yield of 86.6%.

EXAMPLE 9

The procedure of Example 8 was repeated but when the reaction wascompleted the mixture was poured into a solution of 10% aqueoushydrochloric acid with cooling and stirring. The insolubleN-(1-ethylpropyl)2,6 dinitro 3,4-xylidine was extracted with 50 mldichloromethane and washed with a 5% aqueous sodium hydroxide followedby washing with water to neutral. Removal of dichloromethane left thedesired product. The excess of 1-ethyl propylamine was recovered as thesolid chlorohydrate by evaporation of the aqueous solution.

EXAMPLE 10

Example 8 was repeated in every detail except that2,6-dinitro-3,4-dimethyl phenetole was reacted with 1-ethylpropylaminein the presence of 5% mole lithium chloride as catalyst. The yield wasessentially the same.

We claim:
 1. A process for preparingN-alkyl-3,4-dialkyl-2,6-dinitroanilines of the formula ##STR5## whereinR₁ is hydrogen, C₁ to C₆ straight or branched chain alkyl group; andR₂,R₃ and R₄ are independently C₁ to C₆ straight or branched chain alkylgroup optionally substituted by one or more halogen groups,characterized in thata. a 3,4-dialkyl phenol of the formula ##STR6## isselectively nitrated with nitric acid in stage I in a two phase systemto form 3,4-dialkyl-2,6-dinitrophenol of the formula: ##STR7## b. the3,4-dialkyl-2,6-dinitrophenol in stage II is alkylated with analkylating agent in the presence of a base and a catalytic amount of aphase transfer catalyst selected from the group consisting of

    (R').sub.4 Q.sup.+ X--

wherein R' may be the same or different C₁ to C₁₆ straight or branchedalkyl groups, benzyl, substituted benzyl; Q is N or P; and X is Cl, Br,I or HSO₄ ; a macrocyclic ether and polyethylene glycols of formula

    HO--(CH.sub.2 CH.sub.2 O--).sub.n --CH.sub.2 CH.sub.2 OH

where n is an integer from 10 to 50, in an organic solvent to form3,4-dialkyl-2,6-dinitro alkoxybenzene of the formula: ##STR8## where R₅is an alkyl group having 1 to 6 carbon atoms;c. the3,4-dialkyl-2,6-dinitro alkoxybenze is reacted in stage III with anamine of the formula ##STR9## where R₁ and R₂ are defined above, in thepresence of a catalytic amount of base or halide to formN-alkyl-3,4-dialkyl-2,6-dinitroaniline; and d. theN-alkyl-3,4-dialkyl-2,6-dinitroaniline is recovered.
 2. A process inaccordance with claim 1 wherein the mole ratio of phenol to nitric acidin Stage I is from 1:2 to 1:4.
 3. A process in accordance with claim 1wherein the mole ratio of phenol to nitric acid in Stage I is from 1:2to 1:2.5.
 4. A process in accordance with claim 1 wherein the solvent ofStage I is chosen from the group consisting of dichloromethane,1,2-dichloroethane, 1,1,1-trichloroethane, carbon tetrachloride,chloroform, trichloroethylene, tetrachloroethylene, chlorobenzene,dichlorobenzene, benzene, dialkylether and mixtures of these.
 5. Aprocess in accordance with claim 4 wherein the solvent of Stage I isdichloromethane.
 6. A process in accordance with claim 1 wherein thealkylating agent of Stage II is selected from the group consisting ofalkyl sulfate, alkylarylsulfonate, or alkyl halides.
 7. A process inaccordance with claim 6 wherein the alkylating agent of Stage II isdimethylsulfate or diethylsulfate.
 8. A process in accordance with claim1 wherein the phase transfer catalyst of Stage II is an alkyl oraralkylammonium halide.
 9. A process in accordance with claim 8 whereinthe phase transfer catalyst of Stage II is didecyldimethylammoniumchloride, tricaprylmethyl ammonium chloride, or triethylbenzyl ammoniumchloride.
 10. A process in accordance with claim 1 wherein the solventof Stage II is selected from the group consisting of acetone,methylethyl ketone, methyisobutyl ketone, cyclohexanone, cyclopentanone,dichloromethane, 1,2-dichloroethane, methylchloroform, carbontetrachloride, benzene, toluene, xylene, cyclohexane and mixtures ofthese.
 11. A process in accordance with claim 10 wherein the solvent ofStage II is dichloroethane or acetone.
 12. A process in accordance withclaim 1 wherein the amine of Stage III is a monoalkylamine.
 13. Aprocess in accordance with claim 1 wherein the mole ratio of amine toalkoxybenzene derivative of Stage III is from 2:1 to 6:1.
 14. A processin accordance with claim 1 wherein the mole ratio of amine toalkoxybenzene derivative of Stage III is from 3:1 to 5:1.
 15. A processin accordance with any of claim 1 wherein the catalyst of Stage III isselected from the group consisting of sodium hydroxide, potassiumhydroxide, lithium hydroxide, calcium chloride, barium bromide andlithium chloride.
 16. A process in accordance with any of claim 15wherein the catalysts of Stage III is calcium chloride or lithiumchloride.
 17. A process for preparingN-alkyl-3,4-dialkyl-2,6-dinitroaniline of the formula ##STR10## whereinR₁ is hydrogen, C₁ to C₆ straight or branched chain alkyl group; andR₂,R₃ and R₄ are independently C₁ to C₆ straight or branched chain alkylgroup optionally substituted by one or more halogen groups,characterized in thata. a 3,4-dialkyl-2,6-dinitrophenol of the formula##STR11## is alkylated with an alkylating agent in stage I in thepresence of a base and a catalytic amount of a phase transfer catalystselected from the group consisting of

    (R').sub.4 Q.sup.+ X--

wherein R' may be the same or different C₁ to C₁₆ straight or branchedalkyl groups, benzyl, substituted benzyl; Q is N or P; and X is Cl, Br,I or HSO₄ ; a macrocyclic ether and polyethylene glycols of formula

    HO--(CH.sub.2 CH.sub.2 O--).sub.n --CH.sub.2 CH.sub.2 OH

where n is an integer from 10 to 50, in an organic solvent to form3,4-dialkyl-2,6-dinitro alkoxybenzene of the formula: ##STR12## where R₅is an alkyl group having 1 to 6 carbon atoms;b. the3,4-dialkyl-2,6-dinitro alkoxybenze is reacted in stage II with an amineof the formula ##STR13## where R₁ and R₂ are defined above, in thepresence of catalytic amount of base to formN-alkyl-3,4-dialkyl-2,6-dinitroaniline; and c. theN-alkyl-3,4-dialkyl-2,6-dinitroaniline is recovered.
 18. A process inaccordance with claim 17 wherein the alkylating agent of Stage II isselected from the group consisting of alkyl sulfate, alkylarylsulfonate,or alkyl halides.
 19. A process in accordance with claim 18 wherein thealkylating agent of Stage II is dimethylsulfate or diethylsulfate.
 20. Aprocess in accordance with claim 17 wherein the phase transfer catalystof Stage II is an alkyl or aralkylammonium halide.
 21. A process inaccordance with claim 20 wherein the phase transfer catalyst of Stage IIis didecyldimethylammonium chloride tricapylmethyl ammonium chloride, ortriethylbenzylammonium chloride.
 22. A process in accordance with claim17 wherein the solvent of Stage II is selected from the group consistingof acetone, methylethyl ketone, methyisobutyl ketone, cyclohexanone,cyclopentanone, dichloromethane, 1,2-dichloroethane, methylchloroform,carbon tetrachloride, benzene, toluene, xylene, cyclohexane and mixturesof these.
 23. A process in accordance with claim 22 wherein the solventof Stage II is dichloroethane or acetone.
 24. A process in accordancewith claim 23 wherein the amine of Stage III is a monoalkylamine.
 25. Aprocess in accordance with claim 17 wherein the mole ratio of amine toalkoxybenzene derivate of Stage III is from 2.1 to 6.1.
 26. A process inaccordance with claim 17 wherein the mole ratio of amine toalkoxybenzene derivative of Stage III is from 3.1 to 5.1.
 27. A processin accordance with claim 17 wherein the catalyst of Stage III isselected from the group consisting of sodium hydroxide, potassiumhydroxide, lithium hydroxide, calcium chloride, barium bromide andlithium chloride.
 28. A process in accordance with claim 27 wherein thecatalyst of Stage III is calcium chloride or lithium chloride.